Robots have been developed for applications ranging from material transportation in factory environments to space exploration. One area in which mobile robots have been widely adopted is in the automobile industry, where robots transport components from manufacturing work stations to the assembly lines. These automated guided vehicles (AGVs) follow a track on the ground and have the ability to avoid collisions with obstacles in their path. Autonomous mobile robots designed for planetary exploration and sample collection during space missions, such as NASA's Mars Exploration Rover, have also received significant attention in recent years. This attention has resulted in advancement of mobile robot technology and a corresponding increase in the effectiveness of mobile robots in a wide range of applications.
Mobile robot technology has primarily focused on robot designs having a body with wheels for mobility. This has led to advancements in motion planning and control of the rolling wheel. Notwithstanding these developments, wheeled mobile robots have significant deficiencies that have not been adequately overcome. For example, wheeled robots frequently have difficulty traversing rough terrain. While this problem may be reduced by increasing the size of the wheels of the robot, increases in wheel size cause various undesirable consequences including an increase in the overall size and weight of the robot. Further, increases in wheel sizes do not necessarily result in corresponding increases in operational features such as payload capacity. Also, wheeled robots can be adversely affected by harsh operating environments such as heat, chemicals, and the like.
A variation of a wheeled robot that addresses certain difficulties found in harsh environments is described in U.S. Patent Publication No. 2008/0230285 A1, which shares partial inventorship with the present application. The cited application, which is incorporated herein by reference, describes the first vehicle of its kind that combines efficient wheeled locomotion with a hopping capability. The multimodal robot adds hopping and climbing capability to a wheeled robot by attaching the axle to a central leg so that relative movement of the leg and axle can lift axle. A hopping action can be produced by applying sudden downward force to drive the leg against the support surface. Stair climbing is provided by applying a steady force against the support surface to allow the wheels to climb up the vertical riser. The leg also provides additional stabilization for movement across uneven terrain. In one embodiment, the multimodal robot's wheels are mounted on independently-moving axes that have independent parallelogram linkages to permit the wheels to change relative orientations and tilt.
One alternative to the wheeled robot is the rolling robot. A rolling robot is one that rolls on its entire outer surface rather than on external wheels or treads. They tend to be spherical or cylindrical in form and have a single axle, if any axle at all, and an outer surface that is fully involved in the robot's movement. State-of-the-art rolling robots are all based on the principle of moving the center of gravity of a wheel or sphere, which causes the wheel or sphere to fall in the direction of movement and thus roll along. Rolling robots have a number of advantages over wheeled robots including that the components of the robot are enclosed within a shell, so there are no extremities to hang-up on obstacles, they don't fall over, they can travel on soft surfaces, including water, and they can move in any direction and turn in place.
Improvements in methods of locomotion are needed to allow robotic systems to move within environments that are difficult or impossible for currently-used robot locomotion designs to traverse. The following description discloses such improvements.